#7756 fix(slack): skip completed shared app verification setup

Summary

• Skip the secondary Slack setup modal when the shared app and member authorization are already configured.
• Keep the existing repair action for outdated member access, plus custom-app verification and personal account OAuth.

Type of Change

• Bug fix

Testing

• 55 focused tests passed, covering setup completion, outdated member-access repair and retries, missing configuration, loading and failure states, and existing OAuth behavior.
• Repository lint, generated-artifact, and application/API/tool-boundary audits passed.
• Typechecks run in CI.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)